The emissivity of a surface is a measure of its ability to exchange radiant heat with the surrounding. The emissivity of surfaces is an important characteristic both in the laboratory as well as in practical architectural and industrial situations. For instance, because the emissivity of a surface depends critically on the physical and chemical structure, emissivity measurement is an important method for detecting impurities, gauging degree of cleanliness, or otherwise characterizing the surface.
The prior art evidences apparatus for, and methods of, measuring the emissivity of various materials. A common drawback of the prior art is that it usually requires complex equipment, generally only usable under laboratory conditions and the measurement takes a substantial amount of time. In this regard see Vanderschmidt, U.S. Pat. No. 3,277,715 and "Method for Measuring Total Hemispheric Emissivity of Plain Surfaces with Conventional Thermal Conductivity Apparatus" by N. E. Hager, Jr., appearing in the proceedings of the Seventh Conference on Thermal Conductivity, NBS Special Publication 302, U.S. Government Printing Office, 1968, pages 241-246.
Both of the references mentioned above illustrate methods of, and apparatus for, total hemispheric emissivity measurements. However, each requires thermal equilibrium for its measurement as well as knowledge of the temperature of the surface whose emissivity is to be measured. I have found that typically it takes 6-8 hours for thermal equilibrium to be reached and the temperature measurements require equipment which cannot readily be made portable.
Vanderschmidt, specifically, requires the temperature of the unknown surface be known and furthermore requires the use of a thermal electric cooler having water or other coolant circulating therein. It is not apparent an apparatus of this sort can be made portable and/or relatively simple.
In view of the foregoing, it is one object of the present invention to provide an apparatus for, and method of, making total hemispherical emissivity measurements with relatively simple apparatus which may easily be made portable. It is another object of the present invention to provide the foregoing which can accomplish the measurement in a short period of time. It is a further object of the invention, which is capable of the foregoing advantages, and which is further capable of performing measurements under ambient conditions. Still another object of the present invention is to provide an apparatus of, and method, meeting the preceding conditions, which can be applied to test surfaces in situ. The present invention meets these and other objects as is more fully explained below.